Solve for $x$ and $y$ by deriving an expression for $y$ from the second equation, and substituting it back into the first equation. $\begin{align*}3x+y &= 8 \\ -2x-y &= -9\end{align*}$
Begin by moving the $x$ -term in the second equation to the right side of the equation. $-y = 2x-9$ Divide both sides by $-1$ to isolate $y$ $y = {-2x + 9}$ Substitute this expression for $y$ in the first equation. $3x+({-2x + 9}) = 8$ $3x - 2x + 9 = 8$ Simplify by combining terms, then solve for $x$ $1x + 9 = 8$ $1x = -1$ $x = -1$ Substitute $-1$ for $x$ back into the top equation. $3( -1)+y = 8$ $-3+y = 8$ $y = 11$ $y = 11$ The solution is $\enspace x = -1, \enspace y = 11$.